Multi-path wireless channels are capable of large channel capacities, and may be properly exploited through the use of an MIMO (Multiple-Input-Multiple-Output) communication system. An MIMO system employs multiple transmit antennas and multiple receive antennas. Standard IEEE 802.16e, sometimes referred to as Mobile Worldwide Interoperability for Microwave Access (Mobile WiMAX), supports MIMO antenna technology. Future wireless networks will also support MIMO antenna technology. There have been efforts to introduce a unified proposal for the next generation of high performance wireless networks, developed under the guidelines of the IEEE Standards Association and submitted to the IEEE 802.11n Task Group N (TGn). One of the goals is to enable MIMO Spatial Division Multiplexing to provide reliable transmission speeds of up to 315 megabits per second (Mbps) with two antennas, and up to 630 Mbps with larger systems employing more than two antennas.
Access point density in an enterprise WLAN (Wireless Local Area Network) is expected to increase to where the typical distance between an access point and a client may at times be 10 feet or less. As a result, the effect of line-of-sight (LOS) communication is expected to become important. A strong LOS communication link increases spatial signal correlation, so as to diminish the benefit of an MIMO system.
Accordingly, it is useful to provide communication technology in a multiple antenna client that may be configured to perform well when a LOS communication path is dominant. Furthermore, because upgrading an access point to a MIMO system is more expensive than for a client, it is expected that there will be a period of time for which access points have not yet been upgraded from a SISO (Single-Input-Single-Output) system to a MIMO system. Consequently, it is also useful to provide communication technology in which a multiple antenna client is easily configured whether the access point is a SISO system or an MIMO system.